1. Field of Invention
This invention relates to seat belt retractors and more particularly to seat belt retractors designed to wind up two restraining belts.
2. Prior Art
Three point passenger restraining devices consisting of lap and shoulder restraining belts are widely used as restraining systems for the purpose of restraining passengers during vehicle energencies such as collisions, etc. In these three point restraining devices, the useability and storeability of the restraining belts are improved by the instrallation of a retractor system which retracts, by a bias means those portions of the restraining belt not used by the passenger and the majority of both belts when the passenger is not using the restraining belts.
In such three point restraining devices, the installation of a separate restraining belt retractor for each of the lap and shoulder restraining belts is considered to be the most effective method of improving the useability and storeability of the belts. However, a restraining belt retractor system which winds up both restraining belts on a single retractor shaft one over the other without injuring the useability or storeability of the belts has been proposed.
As shown in FIGS. 1 and 2, the two belts retracting type of restraining belt retractor system is designed as follows: The lap restraining belt 10A and the shoulder restraining belt 10B are formed by a single continuous belt which is folded back through an opening 12 in a tongue plate 11. The lap restraining belt 10A and the shoulder restraining belt 10B, which is drawn upwards and is inserted through the slip joint 14 fastened to the upper portion of the side wall of a motor vehicle 13, are wound up on retractor 15. Retractor 15 is fastened to the lower portion of the side wall of a vehicle 13 and is designed so that the lap restraining belt 10A and the shoulder restraining belt 10B are wound up on a single retractor shaft 16 one over the other.
The passenger sitting in the seat 17 puts the three point restraining device into use by engaging the tongue plate 11 with the buckle 18 which is anchored at the approximate center line of the vehicle 13.
The use of said two belts retracting type of restraining belt retractor system makes it possible to simultaneously extend both restraining belts by pulling either one of the restraining belts out of the retractor 15. Furthermore, since one continuous restraining belt is folded back through the tongue plate 11, it is possible to adjust the relative length of each belt so that the lap restraining belt 10A and the shoulder restraining belt 10B are both constantly maintained at an appropriate length for use. Accordingly, such a system has offered superior useability and handling in spite of the fact that only a single retractor is employed.
However, in this two belts retracting type of retractor system, although the lap restraining belt is simultaneously extended when the passenger pulls out only the shoulder restraining belt, there is a possibility that the lap restraining belt will become slack inside the retractor mechanism due to the fact that there is no tension acting upon it (as shown by the broken line in FIG. 2).
A restraining belt in which such slack has been generated may become stuck inside the retractor mechanism or may interfere with the operation of the lock bar 19 which is for instantly stopping the rotation of the retractor shaft in the direction of belt extension during a vehicle emergency. There is also a danger in extreme cases that slack will be generated in one of the restraining belts while it is in use, thereby having a deleterious effect upon the restraining ability of the system so that secure restraint of the passenger is made impossible.
This invention has been designed with the aforementioned difficulties in mind.